Optical sensors, such as optical proximity sensors, may include a light source including one or more light emitting element (e.g., LEDs) and an adjacent photosensitive light detector, where the sensor can estimate proximity of an object based on the magnitude of reflected light from the one or more LED returning to the sensor. The value of these sensors has become more important in the recent past with the advent of battery-operated handheld devices, such as mobile phones. For example, a fair amount of the energy from a mobile phone battery is used to drive the display, and there is value in turning off the display or backlight when the mobile phone or other device is brought to the user's ear (where it cannot be viewed anyway). Optical proximity sensors have been used for this, and many other applications.
For other examples, there are many other applications in which the presence of an object can be detected with an optical proximity sensor to advantage. These range from sensing when protective covers have been opened on machinery, paper has been positioned correctly in a printer, or an operator's hands are at risk near an operating machine. An optical proximity sensor can also be used as a simple touch or near-touch activated switch, and could be implemented in applications like keyboards or devices that have a plastic housing that is sealed but which allows the light from the source to pass through and be sensed by the detector on the return.
Various different forms of optical sensors are available to detect the presence or absence of an object. For instance some optical sensors are configured to sense motion and turn on a light when motion is detected. Some optical sensors are configured to sense ambient light and turn on a light when it is dark. For another example, auto-focus cameras are often configured with an infrared LED and use the light received through the camera optics to perform auto focus in dim light conditions. Further, photo interrupter modules exist in many forms to detect the passage of an object between a light source and a light detector. For example, garage door openers (which are also used to close garage doors) often use an infrared (IR) light source and a remote light detector to prevent objects or persons from being crushed under a closing garage door. These are just a few examples of the various types and uses of optical sensors.